Form in steps, how to ignore some input and move on ?!

var currentTab = 0; // Current tab is set to be the first tab (0)
showTab(currentTab); // Display the current tab

function showTab(n) {
  // This function will display the specified tab of the form ...
  var x = document.getElementsByClassName("tab");
  x[n].style.display = "block";
  // ... and fix the Previous/Next buttons:
  if (n == 0) {
    document.getElementById("prevBtn").style.display = "none";
  } else {
    document.getElementById("prevBtn").style.display = "inline";
  }
  if (n == x.length - 1) {
    document.getElementById("nextBtn").innerHTML = "Cadastrar";
  } else {
    document.getElementById("nextBtn").innerHTML = "Próximo";
  }
  // ... and run a function that displays the correct step indicator:
  fixStepIndicator(n);
}

function nextPrev(n) {
  // This function will figure out which tab to display
  var x = document.getElementsByClassName("tab");
  // Exit the function if any field in the current tab is invalid:
  if (n == 1 && !validateForm()) return false;
  // Hide the current tab:
  x[currentTab].style.display = "none";
  // Increase or decrease the current tab by 1:
  currentTab = currentTab + n;
  // if you have reached the end of the form... :
  if (currentTab >= x.length) {
    //...the form gets submitted:
    document.getElementById("regForm").submit();
    return false;
  }
  // Otherwise, display the correct tab:
  showTab(currentTab);
}

function validateForm() {
  // This function deals with validation of the form fields
  var x,
    y,
    i,
    valid = true;
  x = document.getElementsByClassName("tab");
  y = x[currentTab].getElementsByTagName("input");
  // A loop that checks every input field in the current tab:
  for (i = 0; i < y.length; i++) {
  
    // If a field is empty...
    if (y[i].required && y[i].value == "") {
      // add an "invalid" class to the field:
      y[i].className += " invalid";
      // and set the current valid status to false:
      valid = false;
    }
  }
  // If the valid status is true, mark the step as finished and valid:
  if (valid) {
    document.getElementsByClassName("step")[currentTab].className += " finish";
  }
  return valid; // return the valid status
}

function fixStepIndicator(n) {
  // This function removes the "active" class of all steps...
  var i,
    x = document.getElementsByClassName("step");
  for (i = 0; i < x.length; i++) {
    x[i].className = x[i].className.replace(" active", "");
  }
  //... and adds the "active" class to the current step:
  x[n].className += " active";
}

#regForm {
  background-color: #ffffff;
  margin: 100px auto;
  padding: 40px;
  width: 70%;
  min-width: 300px;
}

input {
  padding: 10px;
  width: 100%;
  font-size: 16px;
  font-family: Raleway;
  border: 1px solid #aaaaaa;
}

input.invalid {
  background-color: #fcb8b8;
}

.tab {
  display: none;
}

.step {
  height: 15px;
  width: 15px;
  margin: 0 2px;
  background-color: #bbbbbb;
  border: none;
  border-radius: 50%;
  display: inline-block;
  opacity: 0.5;
}

.step.active {
  opacity: 1;
}

.step.finish {
  background-color: #4CAF50;
}

<form id="regForm" action="">

  <div class="tab"><b>Dados da Empresa</b>
    <div class="row">
      <div class="col-md-6">
        <p><br><input placeholder="Empresa*" oninput="this.className = ''" required></p>
      </div>
      <div class="col-md-6">
        <p><br><input placeholder="CNPJ*" oninput="this.className = ''" required></p>
      </div>
    </div>
    <div class="row">
      <div class="col-md-8">
        <p><br><input placeholder="Endereço*" oninput="this.className = ''"></p>
      </div>
      <div class="col-md-4">
        <p><br><input placeholder="Complemento" oninput="this.className = ''"></p>
      </div>
    </div>
    <div class="row">
      <div class="col-md-3">
        <p><br><input placeholder="Bairro*" oninput="this.className = ''"></p>
      </div>
      <div class="col-md-3">
        <p><br><input placeholder="Cidade*" oninput="this.className = ''"></p>
      </div>
      <div class="col-md-3">
        <p><br><input placeholder="UF*" oninput="this.className = ''"></p>
      </div>
      <div class="col-md-3">
        <p><br><input placeholder="CEP*" oninput="this.className = ''"></p>
      </div>
    </div>
  </div>

  <div class="tab"><b>Contato / Redes Sociais*</b>
    <div class="row">
      <div class="col-md-4">
        <p><br><input placeholder="Telefone*"></p>
      </div>
      <div class="col-md-4">
        <p><br><input placeholder="Email*" oninput="this.className = ''"></p>
      </div>
      <div class="col-md-4">
        <p><br><input placeholder="Website" oninput="this.className = ''"></p>
      </div>
    </div>
  </div>

  <div class="tab">Birthday:
    <p><input placeholder="dd" oninput="this.className = ''"></p>
    <p><input placeholder="mm" oninput="this.className = ''"></p>
    <p><input placeholder="yyyy" oninput="this.className = ''"></p>
  </div>

  <div class="tab">Login Info:
    <p><input placeholder="Username..." oninput="this.className = ''"></p>
    <p><input placeholder="Password..." oninput="this.className = ''"></p>
  </div>

  <div style="overflow:auto;">
    <div style="float:right;">
      <button class="btn btn-raised btn-danger" type="button" id="prevBtn" onclick="nextPrev(-1)">Voltar</button>
      <button class="btn btn-raised btn-danger" type="button" id="nextBtn" onclick="nextPrev(1)">Próximo</button>
    </div>
  </div>
  <div style="text-align:center;margin-top:40px;">
    <span class="step"></span>
    <span class="step"></span>
    <span class="step"></span>
    <span class="step"></span>
  </div>

</form>